1. Field of the Invention
The present invention relates to a golf ball excellent in abrasion resistance, and more specifically, relates to an improvement in a resin composition to be used for an outer layer of a golf ball.
2. Description of the Related Art
As a base resin used in an outer layer for covering a core of a golf ball, such as a cover layer or an intermediate layer, ionomer resin and polyurethane are used. A thread-wound core or a vulcanized rubber-molded core is wrapped with a resin composition including these resins as a main component.
In the above structure, a cover layer made of ionomer resin as a base resin is widely used due to its excellent resilience and processing characteristics. However, the problems of this kind of the cover layer are pointed out that, because of its high stiffness and hardness, it provides poor shot feeling, insufficient spin performance, and poor controllability.
On the other hand, polyurethane is used as a base resin for constituting a cover layer, because the polyurethane provides improved shot feeling and spin performance as compared with ionomer resin. However, it cannot be said that the cover layer made of polyurethane provides resilience and abrasion resistance enhanced to satisfactory levels. In addition, when polyurethane is used, the golf ball becomes soft. Such golf ball spins much and decrease a launch angle, resulting in a short ball distance.
In an attempt to solve the problems described above, it has been proposed to include fibrous aluminum borate whisker or organic short fiber in the cover layer (Japanese Laid-Open Patent Publication No. 10-137365 and Japanese Laid-Open Patent Publication No. 2002-136618). However, these fibrous substances have small specific surface areas. For this reason, although the fibrous substances are easily dispersed, the large-sized reinforcing materials come to scatter over the resin. When dispersed in the matrix of the resin, the reinforcing materials have small reinforcing effect. Therefore, in order to satisfy a desired mechanical property, it is required to blend a large amount of reinforcing materials. As a result, the resin content in the resin composition becomes low. In this case, there are problems that resilience which is an important property as a golf ball is not obtained and abrasion resistance becomes low because of insufficient dispersion of the reinforcing material.
Further, it has also been proposed to add nanocomposite material such as hydrotalcite or octosilicate as a reinforcing material other than those described above into a resin composition (Japanese National Publication No. 2004-504900). Since the fillers of these types are formed into nano-sized fine particles, it is hard to be dispersed into resins. In particular, such fillers are difficult to be dispersed as particles into hydrophobic resins to be used in forming a cover layer such as ionomer resin and polyurethane. As a result, agglomerated particles are unevenly located in the resin matrix, as is the case of the reinforcing material with a large diameter described above. Therefore, even if these reinforcing materials are used, neither the hardness of desired level nor the desired abrasion resistance is obtained.